Interactions among neurons and between neurons and glia are critical in neural development and in the maintenance of the vertebrate brain. Specific cell surface molecules that mediate cell-cell adhesion have been identified and evidence for their specific roles in neural histogenesis is emerging. The long-term objective of this work is to understand the molecular basis for adhesion between neurons and glia in normal and aberrant brain development and function. Ng-CAM is a glycoprotein found on neurons but not on astroglia. Perturbation experiments with specific antibodies indicated that Ng-CAM is involved in neuron- astroglia adhesion and in the migration of neurons along Bergmann glia. The molecule is also involved in neuron-neuron adhesion and the fasciculation of neurites. Our recent results suggest that the ligands for Ng-CAM on neurons and astroglia are different. The specific aims of this proposal are to characterize structural features of the Ng-CAM molecule that are involved in binding, to identity and, characterize astroglial and neuronal ligands for Ng- CAM and to analyze other molecules that influence neuron-astroglial cell adhesion. Protein chemical and immunological techniques will be used to analyze the structure and binding function of Ng-CAM polypeptides. Ligands for Ng-CAM on neurons and astroglia will be identified by their binding to immobilized Ng-CAM. Glial ligands will also be isolated by selecting molecules that neutralize the inhibition by anti-astroglial antibodies of Ng-CAM binding to astroglial cells. Specific antibodies against ligands for Ng-CAM will be prepared and used to determine their localization in tissues and to evaluate their role in neuron-astroglial cell ad- hesion and granule cell migration in cerebellar explants in vitro. Other molecules that may be involved in neuron-astroglia interactions include cytotactin (a matrix, molecule secreted by astroglia), a neuronal proteoglycan that binds to cytotactin, laminin, fibronectin, and N-CAM. To understand the roles of these molecules in neuron-astroglia interactions in tissue, specific antibodies and binding fragments of the adhesion molecules will be used to perturb cerebellar morphogenesis in vitro and the results of functional assays will be correlated with the amount and distribution of each molecule in the tissues. The findings of these and related studies will form a basis for evaluating the role of Ng-CAM and other adhesion molecules in specific neurological disorders by comparison to the normal phenotype using biochemical, histological and cell biological criteria.